Braking systems are used in a large variety of machines and vehicles to control, slow and stop the machine. Exemplary machines include passenger vehicles, trains, dump trucks, and mining vehicles. Machines increasingly use electric drive systems to provide propulsion for the machine. For example, passenger vehicles may use a hybrid drive system whereby a traditional gasoline powered engine and an electric motor are both used to provide propulsion for the vehicle. Machines, such as a railway engines and off-road vehicles may use a diesel-powered engine to drive a generator, which provides electric power to a motor. The motor then provides propulsion for the machine.
Braking systems may take advantage of components in electric drive systems to provide braking for machines. For example, a hybrid passenger vehicle may include a regenerative braking system whereby the vehicle is slowed by the electric drive system while at the same time a battery in the vehicle is recharged. Railway engines use dynamic retarding to slow the train. Although brake systems utilizing electric drive systems have been used, these systems cannot stop a machine traveling at high speed quickly, nor can these systems consistently slow a heavily loaded machine traveling downhill or in slippery conditions.
Some prior systems include a manual retarder lever that enables the operator to control ground speed by manually selecting the level of retarding or automatic retarder control that automatically controls machine speed based the operator's machine speed setting. The manual or automatic retarder may control an electric retarding system. Additionally, the operator may control a traditional braking pedal to actuate hydraulic brakes. In this way, the operator can manually control both dynamic retarding and hydraulic brakes. However, this configuration may be difficult for an operator to control effectively. For example, if the speed setting lever is set to high, the operator may have to rely more on the service brakes. In a large, heavily loaded machine, this may lead to the service brakes overheating. In addition, excess service brake wear may occur on a machine if the service brakes are used for continuous retarding.
U.S. Pat. No. 20090,179,486 to Ikeda et al., issued Jul. 16, 2009, entitled “BRAKE SYSTEM IN ELECTRIC DRIVE DUMP TRUCK,” discloses a brake system in an electric drive dump truck having a hydraulic brake and a generator-type retarder operated by a brake pedal. However, the Ikeda reference does not disclose how to provide feedback to the truck's operator when the brake system transitions between hydraulic function and retarder function. Nor does the Ikeda reference discuss how the brake system manages the transition between hydraulic braking and retarder operation when the retarder is not available.